In a radio transmitting system such as a mobile phone, a cellular phone and the like, an SIR (Signal to Interference Ratio) is fixed and transmission power control is carried out in accordance with the state of each transmission channel in order to maintain a BER (Bit Error Rate) at a value below a predetermined value.
The transmission power control method includes a closed loop transmission power control and an open loop transmission power control.
The closed loop transmission power control is a method for controlling transmission power based on the contents of a TPC (Transmit Power Control) command where SIR corresponding to reception quality of a transmitting signal from one end is measured at the other end of communication and the TPC command, which reduces transmission power when a measured SIR value is higher than a target SIR value and which increases transmission power when the measured SIR value is lower than the target SIR value, is transmitted through an inverse channel.
On the other hand, the open loop transmission power control is a method for controlling a transmission power value in such a way that a reception level is subtracted from the known transmission level of the other end of communication to calculate a level lost in a radio section and a target reception level of the other end of communication is added to the lost level.
Here, data communication in which the information amount of a forward link is greatly larger than that of a reverse link is expected to be mainstream in the future, and the development of a radio communication system of asymmetrical communication where the information amount of the reverse link is asymmetrical with respect to that of the forward link is proceeding.
In the case of the radio communication system where the information amount of the reverse link is symmetrical with respect to that of the forward link, since a time difference between transmission timing and reception timing is small, transmission power can be controlled for each slot with high accuracy.
However, in the radio communication system that performs asymmetrical communication where a time difference between transmission timing and reception timing becomes large, a method for controlling transmission power for each slot with high accuracy has not been disclosed yet.